A very big Freenet node, such as the one run at
http://Ubernode.org∞.
Connecting to one may improve performance, but the current infrastructure of Freenet .7 is designed around exchanging references with people you trust. Exchanging references with ANY strangers, including an Ubernode, is less safe, since any of your peers can spy on your requests if he is
really clever - and no matter how good we make the security, you will always be more vulnerable to your peers than to people you are not connected to.
Ubernodes may additionally be able to do massive traffic analysis, based on the large number of nodes they can connect to, but this traffic analysis could just as easily be performed by running multiple smaller nodes.